From about 4500 BC there are settlements on the edges of the marshes where the Tigris and the Euphrates reach the Persian Gulf. Mesopotamia, the region between these two rivers, will be the area of one of the world's first two civilizations, the other being Egypt. Both are established a little earlier than 3100 BC.

Unlike Egypt, where a stable society is established along hundreds of miles of the Nile, Mesopotamia will be characterized by constant warfare and a succession of shifting empires. Towns here shelter within thick protective walls.

Sumer and Gilgamesh: 3100-2500 BC

Sumer, close to the mouths of the Tigris and the Euphrates, is where the first Mesopotamian towns develop. Each grows up round a local temple, which acts as the centre of the region's economic activity. The Sumerian temple priests, needing to keep accurate accounts, are the first people to develop a system of writing.

The region can also claim other significant innovations. The first known potter's wheel, dating from around this period, has been found in Mesopotamia. And a Sumerian ruler, the semi-historical Gilgamesh, is hero of the world's earliest surviving work of literature, the Epic of Gilgamesh.

Gilgamesh is listed in later Sumerian records as the king of Uruk and builder of its great city wall. He may be largely legendary, but his city is real enough as an early centre of civilization. The wall, dating from a little after 3000 BC, is about six miles long. And it is from Uruk that the earliest written tablets survive.

Uruk is soon eclipsed by a neighbouring city state - that of Ur, famous later for its great ziggurat and (in the Bible) as the home of Abraham. The discovery of The royal cemetery at Ur has revealed an astonishing level of sophistication in objects created in around 2500 BC for the local ruling family. But in about 2300 BC both Ur and Uruk yield to a conqueror from beyond Sumer.

Sargon and Akkad: c.2350 BC

The conqueror of Ur is a usurper, which is no doubt why he adopts the name Sargon - meaning the 'true king'. He is Semitic in origin, and tradition states that he begins life as a fruit grower. He gradually conquers the Sumerian cities - first Kish, then Uruk, then Ur - before founding a capital city of his own, Akkad. He then adopts a new title, 'King of the Nation'.

His is the first Semitic dynasty in history, and his civil servants use a script which is an important innovation in the history of writing. Like the scribes of Ebla, whose archive has recently been discovered, they adapt the Sumerian cuneiform to meet the needs of a Semitic language. Writing systems will often, in later centuries, demonstrate a similar flexibility.

The exact location of Akkad, Sargon's capital, is unknown. Its remains lie hidden somewhere in the region where the Tigris and Euphrates come closest to each other. This is the natural place for a capital city (Babylon, Ctesiphon and Baghdad are later built in the same area). Sargon's achievement has been to establish the first Mesopotamian empire.

There will be many more, but few of much greater extent. The Akkadian sphere of influence, either through direct conquest or effective control of trade, stretches at its peak from the Mediterranean coast of Syria to the head of the Persian Gulf. The empire of Sargon and his descendants lasts for some 150 years, before slowly disentegrating and being overrun by tribes from the north.

Babylon, Assyria and others: from 2200 BC

Over the next 1500 years or more, Mesopotamia goes through many periods of chaos, with small city states struggling for power or for survival. But there are also times of imperial stability, when centralized control is reestablished. The two centres, on which the greatest empires of the region are based, are Babylon and Assyria.

There are also periods when much of Mesopotamia is controlled by powers outside the area, notably the Hittites from the 17th century. And eventually the independence of Mesopotamia is brought to an end by the Persians, who overwhelm Babylon in 539 BC.

It is admittedly a province of considerable importance. The first Hellenistic ruler, Seleucus, makes his capital on the west bank of the Tigris at the point where it comes closest to the Euphrates. From 129 BC a site on the opposite bank of the river is developed by the Parthians as Ctesiphon, a city subsequently much favoured by the Sassanian emperors. But it is not until the Muslim Abbasids are established in AD 750 a few miles upstream, at Baghdad, that Mesopotamia regains its full glory as an imperial centre.